Matrix metalloproteinase-9 (MMP-9), a proteinase containing Zn²⁺ mostly expressed in macrophages, has involved in synthesis and degradation of extracellular matrix, as well as regulation of inflammatory mediators, which facilitated the initiation and exacerbation of atherosclerosis and vascular wall remodeling, leading to the occurrence of cardiovascular events. In this review, we focused on the research progress of MMP-9 in atherosclerosis and introduced the predicting value of MMP-9 for acute myocardial infarction and cardiac remodeling of post-myocardial infarction.